Glycerol is a long known chemical compound having the structure shown in the formula below.

Glycerol, which is also known as glycerin or propane-1,2,3-triol, is in the general category of polyol compounds (i.e., compounds containing multiple hydroxyl groups) and finds application in many fields. For example, glycerol is used in many medical, pharmaceutical, and personal care preparations as a lubricant and a humectant, as an organic synthesis building block, as a food additive (e.g., humectant, solvent, sweetener softener, filler, or thickener), as an animal food ingredient, as a plasticizer and softener in plastics and cellophanes, and as an additive or in the preparation of many products, such as nitroglycerin, yarn, fabric, detergent, preservatives, antifreeze, and tobacco products.
In likely its most recognizable derivatives, glycerol forms the backbone of triglycerides, which are esters of glycerol and fatty acids. Thus, lipids sources (e.g., vegetable oils and animal fats) present a ready source of glycerol, which can be produced via saponification (such as in soap-making processes) or transesterification (such as in the production of biofuels).
As seen by the above multiple possible uses, glycerol is a marketable commodity; however, recent increases in the production of waste glycerol, such as in the production of biofuels, has led to an ever-increasing supply of crude glycerol, which is not in a pure form ready for such uses. Rather, crude glycerol must undergo refining and other purification steps to provide glycerol of sufficient purity for marketability, and such necessary treatments are generally found to be cost prohibitive. As a result, most crude glycerol presently being produced is merely discarded as a waste product.
Biofuels are gaining increasing popularity as an alternative to petroleum-derived fuels, particularly in light of increasing prices of crude oils and the fuel products based thereon (e.g., gasoline, diesel, and jet fuels). Biodiesel is one of the first biofuels to gain popularity as an alternative to petroleum-based fuels. During the manufacture of biodiesel via transesterification of plant oils, such as rape, soya, and palm oils, glycerol is produced as a by-product. For example, transesterification of triglycerides (e.g., from vegetable oils or animal fats) typically proceeds according to the reaction shown below,
wherein each R represents hydrocarbon (e.g., a long chain fatty acid) and FAME represents a fatty acid methyl ester (i.e., the biodiesel molecule). Common base catalysts are potassium hydroxide and sodium hydroxide. According to such reactions, approximately 100 kg of glycerol is produced for every 1 ton of biodiesel prepared. In a large-scale biodiesel facility, crude glycerol production can be on the order of millions of gallons per year. While biofuels are praised for their environmental benefits and economic viability, an increasing concern is what to do with the glycerol by-product. Moreover, as industrialized nations attempt to move from fossil fuels to more sustainable alternatives, there is an increasing global excess of crude glycerol.
It was estimated in 2007 that glycerol production in the United States averaged more than 350,000 tons per year, and European production of glycerol was estimated to be around 600,000 metric tons per year. This glycerol supply is also expected to continue to increase as Europe implements directives with mandatory minimum biofuel incorporation into retail fuel supplies. EU directive 2003/30/EC, for example, targets 5.75% biofuel incorporation to be achieved by the year 2010. In light of this growing glycerol supply, there is an on-going search for value added alternatives to disposal.
One alternative to disposal, particularly in association with biofuel production, is glycerol combustion as a heat source for the biofuel production process itself. Combustion of glycerol has been described as an elegant solution to the production of waste glycerol—if it worked well enough. Previous attempts to use waste glycerol as a heating fuel have had limited success and lacked true cost benefit. For example, there has been a long-standing fear that combustion of glycerol releases toxic acrolein gas unless carried out at a sufficiently high temperature. Moreover, scholars in the field have theorized that complete and clean combustion of glycerol by-product requires a burning temperature in excess of 1,000° C. and a relatively long mean residence time in the combustion chamber. Otherwise, effective combustion of glycerol generally requires combination with another fuel source, such as forming “logs” from glycerol and sawdust in a combustible container (e.g., an empty milk carton). Previous attempts to burn glycerol simply have not been able to overcome the safety and technical problems.
In light of the above, there remains a need in the art for viable alternatives to disposal of waste glycerol, such as glycerol by-product from biofuel production. The present invention solves this problem.